[jnaddef]

You should probably stop thinking about your velocity for a while and instead focus on quality.

For your design phases, think thoroughly about all possible solutions and detail the pros/cons of each, then get it reviewed by your colleagues and iterate on that. The design phase might be slow, and it is OK. At least when you will end up implementing something it is likely to be of much better quality.

After a while this will become natural and your velocity will naturally go up.